This invention relates to a valve closure element or "obturator" for control of fluid flow within a valve. In particular, this invention relates to a valve closure element effective over a wide temperature and pressure range which typically interacts with a ring-type seal assembly to close the valve.
A ball valve is described in U.S. Pat. No. 3,515,371. A closure element in the form of a ball with a through aperture is pivoted about a vertical axis 90.degree. to move from a closed to an open condition. The closure element is also pivoted slightly about a horizontal axis to press tightly against a valve seat. The closure element provides an annular band or sealing surface having a spherical or conical or other contour which mates with an annular valve seat. For an understanding of the operation of this ball valve and all relative component parts, U.S. Pat. No. 3,515,371 is herein incorporated by reference. The closure element need not be spherical as demonstrated by U.S. Pat. No. 2,076,840.
It has been experienced that during valve operation, when fluid pressure is applied against the closure element when in the closed position from the seating side of the closure element, the closure element experiences some distortion due to the fluid pressure applied. This distortion results from unequal strength or rigidity caused by unsymmetrical sections of the closure element. Such distortion can result in leakage at the 3 o'clock and 9 o'clock position of the closure element sealing surface.
FIG. 1 shows the effect of pressure on the configuration of the sealing surface. It is to be noted that at the 3 o'clock and 9 o'clock positions, position "A" in FIG. 1, the sealing surface is bowed (the bowed portion exaggerated for clarity) compared to the smaller distortion at the 12 o'clock and 6 o'clock positions at "B" and "C". In other words, a circumference "E" drawn around the sealing surface at its mean radius from a centerline of the closure element diverges from a plane to a bowed configuration. This bowing can cause leakage.
This bowing is due to the increased rigidity of the core element 10 in the top and bottom regions as compared to the center regions which are relatively weakened due to a through bore 14 formed through the core element.